Correlated light and electron microscopy of cell division in large marine oocytes, eggs, and embryos

The rapid and synchronous divisions of large and transparent oocytes, eggs, and embryos of marine species are exceptionally well suited for microscopic observation. Consequently, these cells have been models for cell division research since its beginnings and contributed some of its first and most fundamental discoveries. While large size and rapid transitions render these cells ideal specimens for light microscopy, the same features constitute a challenge for electron microscopy. Here, we describe example protocols from our work on starfish oocyte meiosis, where we overcome these challenges by using live imaging of fluorescently labeled structures in combination with correlated electron microscopy. In this work, we demonstrate how: (i) to capture a rapid, transient event in time and (ii) to localize a small structure within the large oocyte. These techniques are applicable with minor modifications to oocytes and embryos of other species and, possibly, to other cell types.